1. Field of the Invention
The present invention relates to an automatic transmission apparatus transmission control valve operating actuator disposed in an automatic transmission apparatus of an automobile to operate a transmission control valve for controlling a transmission mechanism.
2. Description of the Related Art
Conventionally, in automatic transmission apparatuses in automobiles, particularly in continuously variable transmission control apparatuses, a rotational velocity ratio between an engine shaft and a drive shaft is adjusted by changing a diameter ratio between a main pulley and an auxiliary pulley linked by a metal belt. The diameters of the main pulley and the auxiliary pulley are varied continuously by changing a width of a belt groove on each of the pulleys. The widths of these belt grooves are varied by moving a drum disposed on each of the pulleys. Each of the drums is moved by a hydraulic circuit, a transmission control valve for controlling the amount of that movement being operated by an actuator.
A conventional actuator is provided with: a stepping motor having an exterior casing made of a resin, a motor main body disposed inside the exterior casing, and a shaft rotated by the motor main body; a housing made of a resin coupled to the exterior casing; a pipe for operating a transmission control valve by reciprocating in an axial direction relative to the shaft, a base end portion of the pipe being positioned inside the housing and a tip portion of the pipe being disposed so to project outward from the housing; and a power conversion mechanism for converting rotation of the shaft into rectilinear motion of the pipe.
In this conventional actuator, a pressure difference arises between an internal portion and an external portion of the housing as a result of the reciprocating motion of the pipe. Thus, a communicating aperture communicating between the internal portion and the external portion of the housing is disposed through a side wall of the housing to alleviate the pressure difference between the internal portion and the external portion of the housing arising as a result of the reciprocating motion of the pipe and allow the pipe to move smoothly. Furthermore, a filter is disposed in the communicating aperture to prevent contaminants in the oil from entering the housing through the communicating aperture. (See Patent Literature 1, for example.) Patent Literature 1: Japanese Patent Laid-Open No. HEI 11-218218 (Gazette: paragraph 0024; Claims; FIG. 2)
In conventional actuators, one problem has been that a process is required for affixing the filter by adhesive to the communicating aperture disposed in the housing, increasing the number of manufacturing processes, thereby preventing cost reductions.
In conventional actuators, because ferrite magnets are used for magnets therein, another problem has been that reductions in the size and weight of the magnets is not possible, reducing productivity, thereby preventing cost reductions.